The present invention relates to aligning optical components used in fabricating optical devices. More specifically, the present invention relates to a system for prealigning an optical module which carries an optical component.
Optical devices are being increasingly used in various industries and technologies in order to provide high speed data transfer. In many applications there is a transition or an incorporation of optical devices where previously only electrical devices were employed. An optical device typically consists of a number of components which must be precisely assembled and aligned for the device to operate and function efficiently.
Historically, optical devices such as those used in fiber optic telecommunications, data storage and retrieval, optical inspection, etc. have had little commonality in packaging and assembly methods. This limits the general applicability of automation equipment for automating the manufacture of these devices since there is such a disparity in the device designs. To affect high volume automated manufacturing of such devices, parts of each individual manufacturing line have to be custom-designed.
In contrast, industries such as printed circuit board manufacturing and semiconductor manufacturing have both evolved to have common design rules and packaging methods. This allows the same piece of automation equipment to be applied to a multitude of designs. Using printed circuits as an example, diverse applications ranging from computer motherboards to cellular telephones may be designed from relatively the same set of fundamental building blocks. These building blocks include printed circuit boards, integrated circuit chips, discrete capacitors, and so forth. Furthermore, the same automation equipment, such as a pick and place machine, is adaptable to the assembly of each of these devices because they use common components and design rules.
Further complications arise in automated assembly of optical devices. Such assembly is complicated because of the precise mechanical alignment requirements of optical components. This adds to problems which arise due to design variations. The problem arises from the fact that many optical component properties cannot be economically controlled to exacting tolerances. Examples of these properties include the fiber core concentricity with respect to the cladding, the location of the optical axis of a lens with respect to its outside mechanical dimensions, the back focal position of a lens, the spectral characteristics of a thin-film interference filter, etc. Even if the mechanical mounting of each optical element were such that each element was located in its exact theoretical design position, due to the tolerances listed above, the performance specifications of the optical device may not be met.
To appreciate the exacting alignment requirements of high performance optical devices, consider the simple example of aligning two single mode optical fibers. In this example, the following mechanical alignments are required to ensure adequate light coupling from one fiber to the other: the angle of the fibers with respect to each other, the transverse alignment (perpendicular to the light propagation direction) and the longitudinal alignment (parallel to the light propagation direction).
Typical single mode optical fibers used in telecommunications for the 1.3 xcexcm to 1.6 xcexcm wavelength range have an effective core diameter of about 9 microns and an outside cladding dimension of 125 microns. The typical tolerance for the concentricity of the core to the outside diameter of the cladding is 1 micron. Assuming the outside claddings of the two fibers were perfectly aligned such that there was no angular or longitudinal misalignment, the cores may still be transversely misaligned by as much as 2 microns. This misalignment would give a theoretical coupling loss of about 14 percent or 0.65 dB. This loss is unacceptable in many applications. Techniques using active alignment, such as that shown in U.S. Pat. No. 5,745,624, entitled xe2x80x9cAUTOMATIC ALIGNMENT AND LOCKING METHOD AND APPARATUS FOR FIBER OPTICAL MODULE MANUFACTURINGxe2x80x9d, issued Apr. 28, 1998 to Chan et al., can then be employed to improve the coupling efficiency. Other example alignment techniques are shown in application Ser. No. 09/789,125, filed Feb. 20, 2001 and entitled xe2x80x9cOPTICAL MODULExe2x80x9d; application Ser. No. 09/789,185, filed Feb. 20, 2001 and entitled xe2x80x9cOPTICAL MODULE WITH SOLDER BONDxe2x80x9d; and application Ser. No. 09/789,124, filed Feb. 20, 2001 and entitled xe2x80x9cOPTICAL DEVICExe2x80x9d.
In addition to providing an optical module which addresses some of the issues mentioned above, it would also be desirable to provide a system capable of aligning such an optical module.
In one example aspect, an optical alignment system is provided for aligning an optical module of the type which is suitable for use in an optical device. The system includes a reference base having a registration feature that aligns with a registration feature of the optical module. A sensor is configured to respond to light which has interacted with or been generated by an optical element of the optical module. An optical element manipulator moves the optical element relative to the registration features of the optical module.